(Updates for market close)

By Brigid Riley

TOKYO, March 24 (Reuters) - Japan's Nikkei share

average declined for a third straight session on Monday as

uncertainty ahead of a looming deadline for implementing

additional U.S. tariffs sapped investor appetite for riskier

assets.

The Nikkei closed down 0.2% at 37,608.49, while the

broader Topix shed 0.5% to sit at 2,790.88 after hitting

an eight-month peak on Friday.

The Nikkei received some support as a portion of heavyweight

shares saw some buying, with AI-focused startup investor

SoftBank Group climbing 3% to offer the biggest lift.

U.S. President Donald Trump hinted that he would be

flexible regarding a new round of tariffs set to go into effect

on April 2, helping lift the S&P and Dow at the end of the week.

But the benchmark Nikkei index struggled to advance on the

day, seesawing between gains and losses as investors took a

cautious approach to the impending tariff threat.

Many important details regarding the latest tariffs are

still unknown, keeping investors on edge, said Kazuo Kamitani, a

strategist at Nomura Securities.

"There's no way to predict it, so we have no choice but to

wait for the announcement," Kamitani said.

Major semiconductor-related shares dragged on Monday,

tracking their U.S. peers after the Philadelphia SE

Semiconductor Index ended nearly 1% lower on Friday.

Tokyo Electron ( TOELF ) slid 0.8% and Advantest ( ADTTF )

declined 1.2%, while Screen Holdings ( DINRF ) tumbled 3.5% to

become one of the biggest percentage losers on the Nikkei.

Among other big-name shares, Uniqlo parent firm Fast

Retailing ( FRCOF ) erased earlier gains to stumble 0.1%, and

telecoms company KDDI ( KDDIF ) gave up 1.3%. Seven & i Holdings ( SVNDF )

rose 1.8%.

Sumitomo Realty & Development ( SURDF ) surged 10.5%

after Bloomberg News reported Elliott Management Corp has built

a significant stake in the Japanese real estate developer.